1. Field of the Invention
The present invention relates to a multilayer wiring structure and more particularly, to a multilayer wiring structure including a benzocyclobutene resin layer serving as an interlayer insulating layer for adjoining wiring or interconnection layers, which is applicable to a multilayer wiring board and a semiconductor device.
2. Description of the Prior Art
As the recent trend of the increasing operation speed and the increasing integration scale of semiconductor devices, an interlayer insulating material of a multilayer wiring-board on which the semiconductor device chip or chips are mounted has been required to have not only a heat resistance property but also low dielectric-constant, low water-absorption coefficient, high adhesion properties. As an example of the insulating materials having these properties, a benzocyclobutene resin has been known.
Especially, the benzocyclobutene resin has a good adhesion property to copper (Cu) and has no tendency of the electromigration phenomenon to copper. Therefore, a multilayer wiring board having the benzocyclobutene resin as the insulating material was developed, in which wiring layers contain copper as a primary constituent.
FIG. 1 shows a conventional multilayer wiring board, which was disclosed in the Japanese Examined Patent Publication No. 7-19973 published in March 1995.
In FIG. 1, a first-level wiring layer 22 is formed on an insulating base material 21. The wiring layer 22 is formed by a patterned conductor layer containing copper as a primary constituent. The insulating base material 21 is usually made of silicon, saffhire, or ceramic containing alumina or the like as its primary constituent.
An interlayer insulating layer 23 made of a benzocyclobutene resin is formed to cover the first-level wiring layer 22. The layer 23 is contacted with the exposed area of the base material 21. The layer 23 has a penetrating via hole 24 through which the first-level wiring layer 22 is electrically interconnected with a second-level wiring layer 25.
The second-level wiring layer 25 is formed on the interlayer insulating layer 23 to be contacted with the underlying first-level wiring layer 22 through the via hole 24. The second-level wiring layer 25 also is formed by a patterned conductor layer containing copper as a primary constituent.
Although not shown in FIG. 1, to form a third- and higher level wiring layers, some sets of the interlayer insulating layer 23 and the wiring layer 25 are formed to be stacked on the second-level wiring layer 25 as necessary, thereby constituting a multilayer wiring structure on the base material 21.
As described above, the benzocyclobutene resin has not only a good heat-resistance property but also a low dielectric-constant and a low adhesion property and therefore, it is a good insulating material for an interlayer insulating material of the sort. However, this resin has a problem that it does not have a satisfactory flame-retardant property which corresponds to the V-0 class in the Underwriters' Laboratories (UL) 94 standard.
Specifically, for an electronic equipment which generates a large amount of heat, consumes a large amount of electric power, and requires severe reliability (for example, a mainframe computer), the conventional multilayer wiring board shown in FIG. 1, which contains the interlayer insulating materials made of the benzocyclobutene resin, cannot be applied.
With conventional multilayer wiring boards applicable to the electronic components of this sort, to realize a satisfactory flame-retardant property corresponding to the V-0 class in the UL 94 standard, an epoxy or polyimide resin containing any flame-retardant agent has been used as the interlayer insulating material for electrically insulating adjoining wiring layers.
Similarly, if a suitable flame-retardant agent is added to the benzocyclobutene resin, it may have a satisfactory flame-retardant property corresponding to the V-0 class in the UL 94 standard. However, another problem that the inherent properties of the benzocyclobutene resin degrade due to the addition of the flame-retardant agent will take place.